But hold off on the celebrations, because there was only a modest improvement in vacancies and asking rents. The recovery still looks fragile.

“For much of the year, the strong leasing was almost completely offest by new space coming onto the market,” said the report, released Tuesday. Vacancy rates, fell by 0.4 percent, to 10.5 percent in the fourth quarter from 10.9 percent in the one preceding it. But average asking rents were up less than 1 percent in that same period, to $54.34 a square foot.

Eyes ahead, though, because there are also troubling signs that the pace of activity could slacken this year.

In a briefing to journalists, Mr. Harbert said if unemployment doesn’t start catching up, “we could see a little flattening.”

Moreover, much of the rush for space–especially earlier in the year–came when rents were cheap and concessions generous. Landlords are just starting to scale back on things like free rent and fancy renos, and are nudging asking rents up in prime buildings, brokers at the briefing said. Building owners will need to do some fancy footwork next year to keep pushing rents upward without scaring off tenants.

The report predicts that asking rents will remain stable and vacancies will decrease. “With little construction in the pipeline,” it says, “vacancy rates are projected to decline in 2011.”